WASHINGTON -- Everything for the Nationals begins with their starting rotation. When they are functioning like a well-oiled machine like they have for seemingly the entire month of October -- ripping through the National League and matching a postseason record with an eight-game winning streak -- it is in large part because they have been carried by the arms of their starting pitching.

In no game during this World Series would the advantage in starters be more pronounced than in Game 4, with the Astros starting rookie Jose Urquidy as the beginning of a bullpen game, while the Nationals countered with Patrick Corbin, whom they signed to a $140 million deal to be their third ace, someone they could lean on in games like this. Yet, Corbin was not at his best in an 8-1 loss on Saturday night at Nationals Park, and Washington’s winning formula to upset Houston broke down quickly from there.

So while there are many reasons why this World Series is tied at two games apiece -- the Nationals’ lack of hitting with runners in scoring position, the talent level of the Astros, and manager Dave Martinez leaving his highest leverage relievers in the bullpen, to name a few -- the Nats were counting on Corbin to be an ace in Game 4, and he was not at his best.

“They are a tough lineup,” Corbin said. “They are one of the best in baseball. Try to just minimize damage there, we were still in the game there a little bit. We had our chances yesterday, and our chances today, things just didn’t go our way, unfortunately.”

• How Nats' chance for G4 rally slipped away

The game was certainly not lost entirely by Corbin, who gutted through six innings of four-run ball on the mound, even when he was not at his sharpest.

But the Astros came out more aggressive than he anticipated in the first inning, collecting four singles to score a pair of runs and put the Nationals behind from the jump. Corbin, who was able to limit the damage thanks to some stellar defense, kept them off the board until Robinson Chirinos’ two-run homer in the fourth inning.

Corbin had allowed seven hits with five strikeouts and two walks, but when the pitcher’s spot came up in the bottom of the sixth, the Nats chose to pinch-hit for him.

And after spending all month going to great lengths to avoid the middle of their bullpen -- calling starters into relief on their throw day, asking for multiple innings from Sean Doolittle and Daniel Hudson, and using their top six pitchers to eat up nearly 90% of their innings in the postseason rounds leading up to the World Series -- Martinez felt he had to turn to his middle relief with Washington down 4-1 in the seventh.

“For me, you don't chase wins,” Martinez said.

So he started the seventh inning with Tanner Rainey and then turned things over to Fernando Rodney. The result was a combined five walks and an Alex Bregman grand slam that put the game out of reach.

The Astros presented a difficult matchup for Corbin from the start. Their offense is historically good, and Houston was the best team in baseball against lefties, leading the Majors with a 131 wRC+ and going an MLB-best 38-11 when facing lefties in the regular season (now 3-1 in postseason). The Astros also were the best hitting team in baseball against sliders, Corbin’s primary pitch, and by a wide margin.

After Houston laid off a few tough sliders in the first inning, Corbin was forced to mix his pitches a little more evenly, relying on his sinker (31) about as much as his slider (30) while mixing in changeups and fastballs.

“I think that was kind of an in-game adjustment we tried to make,” catcher Yan Gomes said. “We were throwing some sliders, and they weren’t really biting on it. And they were being aggressive, so we had to kind of try to mix and match a little bit, throw his changeup and curveball a little bit more. I think he did a good job of settling in, getting some good innings in, giving us a good chance to fight back.”

Corbin’s sharpness and command has varied at times during this postseason run. He’s appeared lights-out at times; other times, less so. Corbin has also endured the most unusual postseason schedule among any of the Nationals' starters. Saturday was only his third start of the postseason compared to four relief appearances, including a scoreless inning to help the Nats win Game 1.

Corbin had been the Nationals' most flexible pitcher during this postseason run, but on Saturday, they were hoping he would flip back to being a dominant starter. The limits of their winning formula got exposed when he was not.

“I think Pat's still Pat,” Gomes said. “I think he's still going to come out and do his thing. He's done a lot for this team that has been asked of him. He's pitched in quite [a lot] of situations, he's not very used to it. I don't think he'd ever give that as a way out for him. He still wants the ball every time.”